Production of propionic acid by immobilized cell fermentation of cane molasses in an inner plant fibrous-bed bioreactor

A novel method of comprehensively utilizing the sugar-industry by-products to produce propionic acid economically and efficiently was developed. In this method, the by-products of sugar-refinery, sugarcane bagasses and cane molasses, were used as cell immobilized material and carbon source, respectively, for propionic acid production. An inner plant fibrous-bed bioreactor (IPFB) with sugarcane bagasses as support for the immobilization of the fermentation was established. Using the non-treated cane molasses and hydrolyzed cane molasses as carbon source, respectively, Propionibacterium freudenreichii CCTCC M207015 as the fermentation strain, the propionic acid fermentations were conducted. When the non-treated cane molasses was used as carbon source, after 254 h fermentation, 52.39 g middot;L^-1 of propionic acid can be obtained from the IPFB with a productivity of 0.21 g·(L middot;h)^-1; while when the hydrolyzed cane molasses was used, the maximum propionic acid yield reaches 75.18 g·L^-1 after 254 h fermentation and with a productivity of 0.30 g·(L·h) ^-1, the ratio of propionic acid to total organic acids is approximately 83.10%(w/w). The IPFB exhibits excellent production stability during several batches fermentations and the propionic acid yield remains high after ten batches of propionic acid fermentation. The SEM micrograph of the immobilized cells shows that there are numerous cells absorbed onto the surface and apertures of the cane bagasses, which effectively realize the high-density cell fermentation of propionic acid.